Various types of compact devices such as cellular telephones, and electronic data-books equipped with liquid crystal displays and keyboard panels have been developed and put into general use with advances in electronics technology in recent years. These devices are principally composed of two members, which are pivotally interconnected so that they may be unfolded open to a specific size to make the device easy to operate when the device is in use. The two members may be folded closely to permit compact storage of the device, to avoid malfunction of keyboards, and to avoid damages to the liquid crystal displays when the device is carried in a bag or in a pocket.
For example, in a conventional cellular telephone, a main body having a keyboard and a transmitter having a microphone are pivotally interconnected. The transmitter may be closed for carrying convenience and to cover the keyboard (hereinafter, this position will be referred to as the "closed position"), and may be opened to allow operation via the keyboard when the telephone is in use (hereinafter, this position will be referred to as the "opened position"). A conventional electronic data-book also has a main body having a keyboard and a liquid crystal display pivotally interconnected with the main body. A conventional cosmetic compact also has a case for accommodating a puff and a mirror pivotally interconnected to the case.
Typical hinge devices adapted for these devices pivotally connect the main body and the cover in simple manners. When a user releases a lock mechanism between the main body and the cover, the cover is automatically rotated to the closed position by means of, for example, a spring. A user closes the cover against the biasing force by the spring, at which position the cover is locked with the main body by means of the lock mechanism.
The prior hinge device has a stopper for engaging the cover with the main body at the opened position, as well as the lock mechanisms for locking the cover with the main body at the closed position. The stopper is disposed adjacent to the pivot in order to reduce the size of the hinge device, and the cover or the stopper may be damaged because of excessive stress arising from the engagement between the cover and the stopper.
In addition to the above disadvantages, the prior hinge devices have not allowed adjustment of the cover with respect to the main body at any chosen angle. Although the prior hinge devices have performed quite well in the engagement of the cover at the opened and closed positions, an additional engaging means is required to hold the cover at any chosen angle. The need has therefore arisen for a hinge device which allows for a variety of selectively variable rotated positions in which, for example, a movable transmitter of a cellular telephone or a movable liquid crystal display of a electronic data-book can be held and maintained.
Furthermore, it has become increasingly desirable to provide a hinge device which has a biasing means for biasing the cover toward the closed position when it is slightly opened whereas biasing the cover in a direction of the opened position when it is close to the opened position. Particularly, it is desirable to provide a cellular telephone in which the cover is automatically moved to the closed position when a user slightly closes the cover after a call and in which the cover is automatically moved to the opened position when he opens the cover to use the telephone.
However, the prior hinge devices have not provided the above-mentioned function because biasing the cover in both directions of the opened and closed positions is impossible although biasing the cover in one rotational direction is possible.
Some devices employ friction hinge devices as a means capable of locking the cover at any chosen angle with respect to the main body. The prior friction hinge, however, cannot achieve the above-mentioned function because it provides a regular friction force against the cover throughout any angle.